E-commerce has so far been the success story of a tumultuous holiday spending season. But as the season progresses, some experts said the advantage may shift to brick-and-mortar stores more heavily than in past years.

Following a solid Cyber Monday—which logged the heaviest online spending numbers in history, increasing by 18 percent to $1.74 billion, according to comScore—some analysts said that frenzied shoppers will likely turn to physical stores for last-minute purchases.

Noting that this year has six fewer days between Thanksgiving and Christmas than last year, Citi analysts Oliver Chen and Kate McShane wrote in separate notes on Tuesday that late shoppers' anxiety over shipping speed could send more of them to stores to avoid worries that online buys may not arrive by Christmas.

"With the shortness of the holiday season, brick-and-mortar stores might be winners because of the likelihood of last-minute buying," McShane wrote.

A study by analytics firm ShopperTrak said that it expects to see more shoppers making late purchases this year, and the last four days before Christmas will be among the 10 busiest. That might be one reason why, Kohl's announced Thursday that for the first time it will be open 24 hours a day leading up to Christmas, starting at 6 a.m. Dec. 20 and ending at 6 p.m. on Christmas Eve. Other retailers may follow suit.

ShopperTrak founder Bill Martin said that despite a busy end to November—caused by the late Thanksgiving—the majority of holiday sales actually occur in December. This year, he predicts about 55 percent of the season's sales will come from December.

"Calendar changes affect each holiday season differently," Martin said in an October release. "Because Christmas falls on a Wednesday this year, it will create its own mid-week momentum without compromising the typically high weekend shopper activity."

Kantar Retail's Anne Zybowski said she thinks shoppers will "absolutely" push their spending back this season, because although people in the retail industry know the season is six days shorter, she's not sure that shoppers are aware.

A survey by the National Retail Federation backed up the thesis of people holding back on some purchases until December, saying that as of the end of Black Friday weekend, only 11 percent of shoppers had finished their holiday shopping.

But not everyone agreed the shorter calendar would impact brick-and-mortar sales.

Forrester analyst Sucharita Mulpuru said shoppers know they must get their orders in by a certain time to meet shipping deadlines. She pointed out that carriers offer Sunday delivery during the holiday season, and said that most people trust Amazon for fast delivery, which is where many go for last-minute purchases anyway.

This will become even truer in 2014, when Amazon rolls out Sunday delivery of packages with the U.S. Postal Service to select cities, said Craig Johnson, president of Customer Growth Partners. He agreed with Mulpuru, saying that people don't just wake up one day and realize it's almost Christmas.

"The idea of a nominally shorter holiday season—we think that's bogus," he said.

Zybowski, however, said that aside from reliable websites like Nordstrom.com, Amazon is a different animal than most traditional retailers. She said there is often a delay between when an order is placed and when it is fulfilled, and many retailers don't start the delivery clock until the order has already been shipped. Delivery windows are also a cause of anxiety for shoppers because they may not offer a specific delivery date or the promised time involves only business days.

"Unless they've had a good experience ... they're probably quite hesitant to order from [them] in December," she said.

A snapshot of December 2012 standard shipping delivery rates

Company

Delivery times

Amazon

2.7 days

Best Buy

7.7 days

Staples

1.0 days

Target

3.7 days

Toys "R" Us

3.0 days

Wal-Mart

4.0 days

Source: StellaService

According to data from StellaService, which evaluates customer service from thousands of retailers, purchases made with standard shipping rates at Amazon last holiday were delivered in an estimated 2.7 days. While that is a quick turnaround and a plausible option for some late shoppers, some brick-and-mortar stores lagged, with Target taking an average 3.7 days for delivery, Wal-Mart four days, and Best Buy 7.7 days.

Mulpuru said it's typical to see a drop in online sales about six or seven days before Christmas, about two or three days sooner than in-store purchases.

And if fewer days don't discourage shoppers from online purchases, the shipping costs associated with quicker shipping may. These costs along with the likelihood of not getting a package on time, influence some shoppers not to buy online, she said.

Of course, some online retailers mitigate the cost factor by sometimes offering express shipping for standard rates or through programs such as Amazon's Prime service, which gives subscribers free two-day shipping on millions of items.

(When shoppers see shipping dates, as shown in the image above, they may realize that this year's compressed calendar may not give them enough time to receive their purchases, and that could influence their choices of where to buy their gifts, analysts said.)

Another option for shoppers at bricks-and-mortar stores such as Gap and Nordstrom is to place their orders online and pick up the items in store. However, Zybowski warns it's often hard to utilize these options from apparel retailers because certain sizes may be out of stock.

Mulpuru pointed out that shoppers who wait until the last minute run the risk of being left with "a bunch of junk that nobody wants to buy," whether it's at a physical store or online.